(1) Field of the Invention
The present invention relates to a device that is associated with gas well heads or portions of damaged gas piping that provides for enhanced worker safety with respect to hazardous gas levels encountered when performing maintenance tasks on hazardous gas containing piping and wells.
(2) Description of the Art
Decomposing materials at landfills produce methane and other valuable gases. It has become common to recover use the valuable components of landfill off gases using gas recovery wells. Landfills, however, are increasingly experiencing higher levels of hydrogen sulfide gas comingled with landfill gas (LFG) at sites across the country. These higher levels of hydrogen sulfide as well as methane and other combustible landfill gases represent a hazard to landfill technicians, contractors and employees as they perform maintenance on LFG recovery wells.
The current practice of installing a gas extraction well in a landfill is to drill a hole into the waste mass and insert a casing bore pipe into the boring (with the lower pipe segment slotted or perforated to allow LFG to enter the pipe from all sides) and solid pipe on the upper segment (to a level 3-4 feet above the surface). Once the pipe is in place the hole is backfilled (excluding the well pipe bore) with stone or gravel to the level of the perforations. Next, a seal is installed to isolate the collection zone (with stone/gravel and perforated pipe) from areas above and backfill the remaining portion of the hole with soil to the surface of the landfill. The bore pipe is then connected to a vacuum source to remove LFG from the bore and adjacent areas and to direct the LFG to recovery processes or to flare.
After installation of a gas extraction well, it is often necessary to perform maintenance on the well such as adding or removing dewatering pumps and in some cases extending the well vertically. These and other maintenance procedures require the operator to temporarily disable the vacuum source to the gas extraction well. When vacuum is not being applied to a gas extraction well, landfill off gases can vent through the open well to the landfill surface in the same area where workers are performing maintenance tasks. The vented gas may contain combustible gases such as methane as well as excessive levels of hydrogen sulfide each of which can cause the work area around the open extraction well to be hazardous.
Hydrogen sulfide (H2S) is especially dangerous. Hydrogen sulfide is a colorless, flammable, extremely hazardous gas with a “rotten egg” smell. It can be both an irritant and chemical asphyxiant and therefore poses a death risk to humans at elevated levels. Hydrogen sulfide gas can be generated in landfills as the result of the decomposition of sulfur bearing wastes following exposure to liquids and organic materials. Because hydrogen sulfide is heavier than air (with a density=1.19 versus air=1.0) it has a tendency to collect in low lying areas such as excavations in waste, poorly-ventilated areas such as leachate collection pump stations and manholes, and may be released from solution in leachate. Hydrogen sulfide can be detected by the human nose at levels as low as 0.0005 ppm. Therefore even very low levels may represent a nuisance odor once it becomes dispersed in the air.
Typically, landfill employees, as well as contractors, working at the landfill on leachate collection or gas collection systems wear personal gas monitoring equipment to detect low oxygen levels and the presence of H2S. They are preset to alarm should H2S levels at or above 10 ppm be encountered. This alarm level is at 10% of the OSHA determined hazard level of 100 ppm which affords personnel ample time to retreat upwind to areas at lower levels. This protects workers from low level exposure and by design dangerous levels of exposure. Indeed, OSHA has established an acceptable ceiling concentration for exposure for an 8-hour shift of 20 ppm with a maximum peak of 50 ppm.
Since personnel working in close proximity to potential sources of hydrogen sulfide gas will have the greatest potential for exposure, coupled with the fact H25 is heavier than air, the greatest risk is therefore to workers at the landfill. Therefore, there is a need for devices and methods that keep the area around landfill gas extraction well and other types of gas wells safe while work is being performed on the wells.